The invention relates to a medical implant and a method for producing an implant of this kind. An implant and a method are each known from DE 10 2007 012 964 A1.
Braided implants such as, for example, braided stents, have the advantage of being flexible and very fine-meshed. This improves the flow control during the treatment of aneurysms and the filter function during the expansion of stenoses. In addition, braided implants comprise closed cells which facilitate the repositioning of the implants since they can be drawn back into a supply system, for example a catheter.
It is known how to form stents from a single wire which changes direction many times and in doing so forms a loop at the ends in each case. The use of a single wire to produce a stent has the drawback that the entire stent has one fixed wire thickness. A further drawback of a single-wire braid consists in the fact that the fineness of the mesh of the stents is limited. In addition, the number of the wire crossovers is limited in the case of production from a single wire.
On the other hand, braided stents produced, for example, with the aid of textile machines from multiple wires have the advantage that different wall thicknesses can be formed within the same stent. The wires with a larger diameter endow the stent with strength in the radial direction. Finer wires produce a fine-mesh structure. The production of a braided stent from multiple individual wires also has the advantage that wires made of different materials can be used, wherein certain materials, such as, for example, nitinol, cobalt alloys, high-grade steel, endow the stent with the necessary strength and other materials, such as, for example, platinum and tantalum, confer X-ray visibility. The high number of wires, and hence the fine mesh structure, is particularly advantageous. It also improves automation of production.
To produce a braided stent, usually a longitudinal round braid is formed which is cut-off or cross-cut at the axial ends. This causes the formation of free wire ends at the axial edges of the stent resulting in various drawbacks:
The wires can separate and hence leave the respective crossover region in the braid. The loose wires may exert no radial force or only reduced radial force which impairs the functionality of the stents when treating aneurysms and stenoses. The free ends result in a risk of injury or risk of inflammation and the formation of stenoses, since they are able to pierce the vessel wall. Further drawbacks of braided stents with open ends occur in conjunction with a supply system, for example a catheter. For example, on crimping, the free ends can become entangled in the supply system with the consequence that the stent fails to open. This results in a risk of coagulation and impaired stent functionality. When the stent is pushed out of the supply system, eg when released by a stabiliser, a compressive force is applied to stent causing the loose wires to be heavily compressed since the structure is not stable, at least in the marginal region of the stent. Hereby, the wires can be damaged and distorted. This results in an increased risk of injury, particularly if the free wire ends are bent radially outward.
Even if no damage or compression occurs on the seating of the stents, the free wire ends can result in impaired functionality, since, due to the relatively unstable structure, the loose wires in the region of the axial stent ends do not have the necessary radial force to expand radially outward after being released from the supply system. Instead, the loose wires protrude into the bloodstream and hence increase the risk of coagulation.
U.S. Pat. No. 4,655,771 counteracts the problem of the loose wire ends in that they are connected by U-shaped connecting members, although this can induce stresses in the stent which can result in the deformation of the stent. In addition, in the case of very fine-mesh stents with a plurality of individual wires, the connection of individual wires by U-shaped connecting means is very difficult or virtually impossible from the production point of view.
U.S. Pat. No. 5,061,275 discloses a stent in which the loose ends are knobs formed by laser treatment in order in this way to counteract traumatisation. Hereby, the stability of the stent is improved by local plastic deformation of the individual wires in the region of the cross-overs or knots in the braid which is complex from the production point of view. In addition, with this stent, the radial force decreases in the region of the loose ends so that there is a risk of their protruding into the bloodstream.
DE 10 2007 012 967 A1, mentioned in the introduction, discloses an implant, for example an inliner or flow diverter embodied as a round braid and in which the individual filament ends protruding at the implant ends are brought together and connected to each other at least in pairs. The connected filament ends are atraumatically reshaped so that the risk of injury is reduced. This does not achieve sufficient improvement to the stability and atraumatic properties of the implant ends, since, on the release of the implant from a supply system, the bunched filament ends can become distorted.